Catalyst for regulating the molecular weight distribution of ethylene polymers

ABSTRACT

A vanadium-based catalyst is treated with certain phosphorus-containing compounds as a means of narrowing and effectively regulating the molecular weight distribution of the polymers produced with the catalyst.

This application is a division of Ser. No. 214,581, filed Jul. 1, 1988,now U.S. Pat. No. 4,886,771.

FIELD OF THE INVENTION

This invention relates to a vanadium-based catalyst suitable forregulating the molecular weight distribution of ethylene polymers.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,508,842 discloses a highly active vanadium-containingcatalyst capable of producing ethylene polymers having a broad molecularweight distribution. Said catalyst comprises:

(A) a solid catalyst precursor consisting essentially of

(1) an inorganic carrier, as support for

(2) the reaction product of (a) a vanadium trihalide and (b) an electrondonor, and

(3) a boron halide or alkylaluminum modifier,

(B) an alkylaluminum cocatalyst, and

(C) a halohydrocarbon polymerization promoter.

The polymers produced in accordance with U.S. Pat. No. 4,508,842 have arelatively broad molecular weight distribution, and excellentextrudability. These properties render them extremely useful in a widevariety of applications, such as wire and cable insulation, blowmolding, film, and pipe fabrication. However, such polymers cannot beused in other applications, such as injection molding, which require anarrower molecular weight distribution.

U.S. Pat. No. 4,514,514, on the other hand, discloses a vanadiumcontaining catalyst useful in the preparation of ethylene polymershaving a narrow molecular weight distribution. Such catalyst comprises:

(A) a solid catalyst component obtained by reacting a tetravalent orpentavalent vanadium halide compound, an organophosphorus compound andan organoaluminum compound.

(B) an organoaluminum cocatalyst, and

(C) a halocarbon polymerization activator.

While the catalysts prepared in this manner have been found useful inthe preparation of polymers having a narrow molecular weightdistribution, such catalysts do not exhibit high polymerization activityunless the vanadium halide compound, organophosphorus compound andorganoaluminum compound employed to produce catalyst component (A) arereacted together under such conditions that catalyst component (A) isprecipitated from solution as a particulate solid. Such procedure,however, results in the formation of irregularly shaped catalystparticles which are undesirable in continuous, commercial polymerizationprocesses, particularly fluid bed polymerizations which require the useof rounded uniform catalyst particles in order to produce roundedpolymer particles necessary to sustain polymerization. Rounded catalystparticles of uniform size are usually and conveniently prepared byimpregnating the catalyst in a porous inorganic carrier, a procedureprecluded by the catalyst preparation process of U.S. Pat. No.4,514,514.

In addition to producing irregularly shaped catalyst particles, thecatalyst preparation procedure of U.S. Pat. No. 4,514,514 requires theuse of specific ratios of aluminum and phosphorus to effectprecipitation of catalyst component (A) from solution. As a result, therelative amounts of aluminum, phosphorus and vanadium in the catalystcannot be varied as desired. This inflexibility limits the use of theorganoaluminum and organophosphorus compounds as catalyst modifiers andthe ability to vary polymer properties through the use of thesematerials.

Japanese Patent Disclosure No. 61-138605, published Jun. 26, 1986, issimilar to U.S. Pat. No. 4,514,514 except that an organoaluminumcompound is not employed in the preparation of the solid catalystcomponent. This patent disclosure does not describe the effect of thecatalyst produced in accordance therewith on the molecular weightdistribution of the polymers produced with it. However, as in U.S. Pat.No. 4,514,514, this disclosure requires precipitation of the solidcatalyst component from solution and does not permit the use of catalystsupports impregnated with such catalysts.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has now been discoveredthat the molecular weight distribution of ethylene polymers producedemploying a vanadium-based catalyst system comprising:

(A) a solid catalyst precursor consisting essentially of

(1) a solid, particulate, porous, inorganic carrier, as support for

(2) the reaction product of

(a) a vanadium trihalide and

(b) an electron donor, and

(3) a boron halide or alkylaluminum modifier,

(B) an alkylaluminum cocatalyst, and

(C) a halohydrocarbon polymerization promoter,

can be narrowed and effectively regulated within a wide range bytreating catalyst component (A) with varying amounts of a-phosphorus-containing compound having the formula:

    (R).sub.3 P=0

wherein:

R is a monovalent hydrocarbon radical free of aliphatic unsaturationcontaining from 1 to 14 carbon atoms, or --OR¹ wherein R¹ is amonovalent hydrocarbon radical free of aliphatic unsaturation containingfrom 1 to 14 carbon atoms.

While catalyst component (A) may be treated with the-phosphorus-containing compound by simply mixing the two in thepolymerization reactor, it is preferred to pre-treat catalyst component(A) with the phosphorus-containing compound before it is added to thepolymerization reactor.

Thus, the catalyst system of the present invention comprises:

(A) a solid catalyst precursor consisting essentially of

(1) a solid, particulate, porous, inorganic carrier, as support for

(2) the reaction product of (a) a vanadium trihalide and (b) an electrondonor,

(3) a boron halide or alkylaluminum modifier, and

(4) a phosphorus-containing molecular weight distribution (MWD)regulator having the formula (R)₃ P=0, wherein R is as defined above,

(B) an alkylaluminum cocatalyst, and

(C) a halohydrocarbon polymerization promoter.

DETAILED DESCRIPTION OF THE INVENTION

As a result of the present invention, it is now possible to effectivelyregulate the molecular weight distribution (MWD) of ethylene polymersproduced by means of a vanadium-containing catalyst system within a widerange by varying the amount of phosphorus-containing compound (R)₃ P=0employed in the preparation of said catalyst system. Surprisingly, thecatalyst systems containing these phosphorus-containing MWD regulatorshave been found be significantly more active than like untreatedcatalyst systems. As a result, it is possible to produce ethylenepolymers by means of these catalyst systems havingnarrow-to-intermediate molecular weight distributions at enhanced levelsof catalyst activity and polymer productivity. By the effective usethese phosphorus-containing MWD regulators together with a suitablechain transfer agent, such as hydrogen, to control the molecular weightof the polymers, it is now possible, by means of this system, to tailorpolymer properties for use in a wide variety of applications.

The polymers produced with the catalyst system of the present inventionhave a molecular weight distribution (MWD), defined as the ratio ofweight average molecular weight to number average molecular weight(M_(w) /M_(n)), of less than 20 to as low as 4. Another means ofindicating the molecular weight distribution of a polymer is by the meltflow ratio (MFR) of that polymer. By melt flow ratio is meant the flowindex : melt index ratio of the polymer, wherein flow index and meltindex are determined in accordance with ASTM D-1238, Conditions F and E,respectively. The polymers produced with the catalyst system of thepresent invention have a melt flow ratio of less than 120 to as low as30. For these polymers, such MFR values correspond to the M_(w) /M_(n)values set forth above.

The polymers produced with the catalyst system of the present inventionhave a melt index of from greater than 0 g/10 minutes to about 500 g/10minutes, usually of from about 0.1 g/10 minutes to about 100 g/10minutes. The melt index of a polymer varies inversely with the molecularweight of the polymer, and is a function of the hydrogen/monomer ratioemployed during preparation of the polymer.

As indicated above, both the molecular weight and the molecular weightdistribution of the polymers can vary widely depending upon the amountof phosphorus containing MWD regulator present in the catalyst systememployed to produce such polymers and the amount of chain transfer agentpresent during polymerization. As a result, a broad variety of polymershaving widely varying properties can be produced.

The polymers produced with the catalyst system of the present inventionare also characterized by a density of from about 0.86 g/cm³ to about0.96 g/cm³. Such polymers generally contain at least 50 mol percent ofpolymerized ethylene and no more than 50 mol percent of polymerizedalpha olefin containing from 3 to 8 carbon atoms and, optionally,polymerized diene. When polymerized diene is present, the polymerordinarily contains from 0.01 mol percent to 10 mol percent of at leastone such diene, from 6 mol percent to 55 mol percent of at least onepolymerized alpha olefin containing from 3 to 8 carbon atoms, and from35 mol percent to 94 mol percent of polymerized ethylene.

Catalyst component (A) consists essentially of:

(1) a solid, particulate, porous, inorganic carrier, as support for

(2) the reaction product of (a) a vanadium trihalide and (b) an electrondonor,

(3) a boron halide or alkylaluminum modifier, and

(4) a phosphorus-containing molecular weight distribution (MWD)regulator having the formula (R)₃ P=0, wherein R is as defined above.

The vanadium trihalide which is reacted with the electron donor in thepreparation of catalyst component (A) is preferable vanadiumtrichloride, although the halogen present in said vanadium trihalide maybe chlorine, bromine or iodine, or any mixture thereof.

The electron donor employed is a liquid, organic Lewis base in which thevanadium trihalide is soluble.

Suitable electron donors include alkyl esters of aliphatic and aromaticcarboxylic acids, aliphatic ketones, aliphatic amines, aliphaticalcohols, aliphatic ethers and cycloaliphatic ethers. Particularlyuseful are alkyl esters of aliphatic carboxylic acids containing from 1to 4 carbon atoms; alkyl esters of aromatic carboxylic acids containingfrom 7 to 8 carbon atoms; aliphatic ketones containing from 3 to 6carbon atoms, preferably from 3 to 4 carbon atoms; aliphatic aminescontaining from 1 to 14 carbon atoms, preferably from 2 to 8 carbonatoms; aliphatic alcohols containing from 1 to 8 carbon atoms,preferably from 2 to 8 carbon atoms; aliphatic ethers containing from 2to 8 carbon atoms, preferably from 4 to 5 carbon atoms; andcycloaliphatic ethers containing from 4 to 5 carbon atoms, preferablymono or di- ethers containing 4 carbon atoms. The aliphatic andcycloaliphatic ethers are most preferred, particularly tetrahydrofuran.If desired, these electron donors may be substituted with one or moresubstituents which are inert under the reaction conditions employedduring reaction with the vanadium trihalide, as well as duringpreparation of and polymerization with catalyst component (A).

The modifier employed in the preparation of catalyst component (A) is aboron halide or alkylaluminum compound having the formula:

    MX.sub.a

wherein:

M is boron or AlR² .sub.(3-a) wherein each R² is an alkyl radicalcontaining from 1 to 14 carbon atoms, which radicals may be the same ordifferent,

X is selected from the group consisting of fluorine, chlorine, bromineand iodine, and mixtures thereof, and

a is an integer having a value of 0, 1 or 2, provided that a is 3 when Mis boron.

Preferably any halide present in the modifier is chlorine, and any alkylradicals present contain from 1 to 6 carbon atoms. Such alkyl radicalsmay be cyclic, branched or straight chain, and may be substituted withone or more substituents which are inert under the reaction conditionsemployed during preparation of and polymerization with catalystcomponent (A). Diethylaluminum chloride is preferred.

The phosphorus-containing compound employed to treat catalyst component(A) so as to regulate the molecular weight distribution (MWD) of thepolymers produced with the catalyst of the present invention has theformula:

    (R).sub.3 P=0

wherein:

R is a monovalent hydrocarbon radical free of aliphatic unsaturationcontaining from 1 to 14 carbon atoms, or --OR¹ wherein R¹ is amonovalent hydrocarbon radical free of aliphatic unsaturation containingfrom 1 to 14 carbon atoms.

R and R¹ are usually alkyl radicals containing from 1 to 14 carbonatoms, preferably from 1 to 6 carbon atoms, or aryl radicals containingfrom 6 to 14 carbon atoms, preferably 6 carbon atoms.

Both R and R¹ may be substituted with one or more substituents which areinert under the reaction conditions employed during treatment of andpolymerization with catalyst component (A).

The phosphorus-containing compounds which can be employed to treatcatalyst component (A) include both phosphine oxides and phosphates.

Among the phosphine oxides which can be employed are triethylphosphineoxide, tri-n-propylphosphine oxide, tributylphosphine oxide,trioctylphosphine oxide, tricyclohexylphosphine oxide,triphenylphosphine oxide and tribenzylphosphine oxide.

Illustrative of the phosphates which can be employed are trimethylphosphate, triethyl phosphate, tributyl phosphate, tri-n-amyl phosphate,trihexyl phosphate, triphenyl phosphate and tricresyl phosphate.

A solid, particulate, porous, inorganic material is employed as carrierin the preparation of catalyst component (A). The carrier serves assupport for the vanadium trihalide/electron donor reaction product, theboron halide or alkylaluminum modifier, and the phosphorus-containingmolecular weight distribution (MWD) regulator. Suitable carriers includeinorganic materials, such as oxides of silicon, aluminum and zirconium,as well as phosphates of aluminum. Usually these materials have anaverage particle size of from about 10 microns to about 250 microns,preferably from about 20 microns to about 150 microns, and a surfacearea of at least 3 square meters per gram, preferably at least 50 squaremeters per gram. Polymerization activity of the catalyst, i.e.,productivity, can be improved by employing a silica support having anaverage pore size of at least 80 Angstrom units, preferably at least 100Angstrom units. The carrier material should be dry, that is, free ofabsorbed water. Drying of the carrier material can be effected byheating, e.g., at a temperature of at least 600° C. when silica isemployed as the support.

Catalyst component (A) is prepared by treating a solid, particulate,porous, inorganic carrier with:

(1) the reaction product of (a) a vanadium trihalide and (b) an electrondonor,

(2) a boron halide or alkylaluminum modifier, and

(3) a phosphorus containing molecular weight distribution (MWD)regulator having the formula (R)₃ P=0, wherein R is as defined above.

The vanadium trihalide/electron donor reaction product is prepared bydissolving at least one vanadium trihalide in at least one electrondonor at a temperature of from about 20° C. up to the boiling point ofthe electron donor. Dissolution of the vanadium trihalide in theelectron donor can be facilitated by stirring, and in some instances byrefluxing, the vanadium trihalide in the electron donor. Up to severalhours of heating may be required to complete dissolution.

After the vanadium trihalide has been dissolved in the electron donor,the reaction product is impregnated into the carrier. Impregnation maybe effected by adding the carrier to the solution of the vanadiumtrihalide in the electron donor, and then drying the mixture to removeexcess electron donor. The carrier may be added alone as a dry powderor, if desired, as a slurry in additional electron donor. Ordinarily thecarrier and the solution of the vanadium trihalide in the electron donorare mixed together in such amounts that, after drying, the carriercontains from about 0.05 mmoles to about 0.6 mmoles of vanadium pergram, preferably from about 0.3 mmoles to about 0.6 mmoles of vanadiumper gram, and most preferably from about 0.3 mmoles to about 0.5 mmolesof vanadium per gram. The impregnated vanadium trihalide/electron donorreaction product prepared in this manner contains from about 1 mole toabout 5 moles, preferably from about 2 moles to about 4 moles, and mostpreferably about 3 moles of electron donor per mole of vanadiumtrihalide. Excess electron donor not actually complexed with thevanadium trihalide may remain adsorbed on the carrier without illeffects.

The boron halide or alkylaluminum modifier is usually added to thecarrier after it has been impregnated with the vanadiumtrihalide/electron donor reaction product. However, if desired, theboron halide or alkylaluminum modifier may be added to the carrierbefore it is impregnated with the vanadium trihalide/electron donorreaction product. Addition of the modifier to the carrier may beeffected by dissolving one or more modifiers in one or more inert liquidsolvents capable of dissolving the modifier, immersing the carrier inthe solution, and then drying the mixture to remove the solvent. If themodifier is applied subsequent to the vanadium trihalide/electron donorreaction product, the solvent must be one which does not dissolve thevanadium trihalide/electron donor reaction product. The carrier may beadded to the solution of the modifier alone as a dry powder or, ifdesired, as a slurry in additional inert liquid solvent. Alternatively,the modifier may be added to a slurry of the carrier in the inert liquidsolvent. Usually the modifier is added to the slurry dissolved inadditional inert liquid solvent, although this is not necessary.Ordinarily the carrier and the solution of the modifier in the inertliquid solvent are mixed together in such amounts that, after drying,the carrier contains from about 0.1 mole to about 10 moles, preferablyfrom about 0.2 mole to about 2.5 moles, of modifier per mole of electrondonor in the vanadium trihalide/electron donor reaction product presentin the carrier (or to be added to the carrier if it is appliedsubsequent to the modifier).

Among the solvents which can be employed to dissolve the boron halide oralkylaluminum modifier are hydrocarbon solvents such as isopentane,hexane, heptane, toluene, xylene and naphtha.

Addition of the phosphorus-containing compound to the carrier may beeffected in the same manner as addition of the modifier, i.e., bydissolving one or more phosphorus containing compounds in one or moreinert liquid solvents capable of dissolving the phosphorus containingcompound, immersing the carrier in the solution, and drying the mixtureto remove the solvent. If the phosphorus-containing compound is appliedsubsequent to the vanadium trihalide/electron donor reaction product,the solvent must be one which does not dissolve the vanadiumtrihalide/electron donor reaction product. While thephosphorus-containing compound is usually applied separately, forconvenience it may be applied together with the modifier in a singlesolution, provided that the modifier and -phosphorus-containing compoundemployed are not reactive with each other. In any case, the carrier maybe added to the solution of the phosphorus-containing compound alone asa dry powder or, if desired, as a slurry in additional inert liquidsolvent. Alternatively, the phosphorus-containing compound may be addedto a slurry of the carrier in the inert liquid solvent. Usually thephosphorus-containing compound is added to the slurry dissolved inadditional inert liquid solvent, although this is not necessary.

The amount of phosphorus-containing compound employed in the preparationof catalyst component (A) depends upon the particularphosphorus-containing compound employed and the molecular weightdistribution desired in the polymers to be produced with the treatedcatalyst. Catalysts of the type employed herein which have not beentreated with a phosphorus-containing compound have been found to producepolymers having a molecular weight distribution (M_(w) /M_(n)) in excessof 10 up to about 22. This corresponds to a melt flow ratio (MFR) inexcess of 60 up to about 130. By treating such catalysts with thephosphorus-containing compounds described herein, however, it ispossible to lower the melt flow ratio (MFR) of the polymers produced upto as much as 50 percent, depending upon the amount ofphosphorus-containing compound employed. Reductions of up to 50 percentin melt flow ratio (MFR) usually require a molar ratio ofphosphorus-containing compound to vanadium trihalide/electron donorreaction product of from about 1:1 to about 15:1, preferably from about2:1 to about 10:1. Lesser amounts of phosphorus-containing compoundbring about lesser reductions in melt flow ratio (MFR). However, greateramounts of phosphorus containing compound have not been found to provideany further reduction in melt flow ratio (MFR). Generally, thephosphorus-containing compound is employed in amounts such as to providea molar ratio of phosphorus-containing compound to vanadiumtrihalide/electron donor reaction product of from about 0.1:1 to about30:1, preferably from about 0:2:1 to about 10:1, depending upon thedesired result.

As previously disclosed, it is also possible to regulate the molecularweight of the polymers produced by the use of a suitable chain transferagent, such as hydrogen, during polymerization. Generally, hydrogen isemployed and added to the reactor in an amount sufficient to produce ahydrogen:ethylene mol ratio of from about 0.00001:1 to about 0.5:1,depending upon the melt index desired in the polymer product. Inaddition to hydroqen, other chain transfer agents may be employed toregulate the molecular weight of the polymers.

The ability to regulate the molecular weight distribution of thepolymers over a broad molecular weight range allows polymer propertiesto be tailored for use in multifarious applications and greatlyincreases the versatility of the catalyst system.

Component (B) of the catalyst system of the present invention is analkylaluminum cocatalyst having the formula

    Al(R.sup.3).sub.3

wherein R³ is a saturated hydrocarbon radical containing from 1 to 14carbon atoms, which radicals may be the same or different. Such radicalsmay be substituted with one or more substituents which are inert underthe reaction conditions employed during polymerization. Preferably R³ isan alkyl radical containing from 2 to 8 carbon atoms.

Component (C) of the catalyst system of the present invention is ahalohydrocarbon polymerization promoter having the formula

    R.sup.4 .sub.b CX'.sub.(4-b)

wherein:

R⁴ hydrogen or an unsubstituted or halosubstituted alkyl radicalcontaining from 1 to 6 carbon atoms, which radicals may be the same ordifferent,

X' is halogen, and

b is 0, 1 or 2.

Preferred promoters include flouro-, chloro- or bromo- substitutedethane or methane at least 2 halogens attached to a single carbon atom.Preferred promoters include CCl₄, CHCl₃, CH₂ Cl₂, CBr₄, CFCl₃, CH₃ CCl₃,and CF₂ ClCCl₃. Particularly preferred promoters are CH₃ CCl₃, CFCl₃,and CHCl₃.

Polymerization is effected, with the catalyst system of the presentinvention by contacting ethylene, or a mixture of ethylene and at leastone alpha-olefin having 3 to 8 carbon atoms, with the three componentsof the catalyst system, i.e., the solid catalyst precursor (treated withthe phosphorus-containing compound), the alkylaluminum cocatalyst, andthe halohydrocarbon polymerization promoter. While polymerization can beeffected employing either solution, slurry or gas phase techniques, itis preferably effected in a fluid bed reaction system. Suitable fluidbed reaction systems are described, e.g., in U.S. Pat. No. 4,302,565,4,302,566 and 4,303,771, the disclosures of which are incorporatedherein by reference.

The solid catalyst precursor, cocatalyst and polymerization promoter canbe introduced into the polymerization reactor throuqh separate feedlines or, if desired, two or all of the components may be partially orcompletely mixed with each other before they are introduced into thereactor. In any event, the cocatalyst and polymerization promoter areemployed in such amounts as to provide a molar ratio of the promoter tothe alkylaluminum cocatalyst of from about 0.1:1 to about 10:1,preferably from about 0.2:1 to about 2:1, and the cocatalyst and thesolid catalyst precursor are employed in such amounts as to provide anatomic ratio of aluminum in the cocatalyst to vanadium in the precursorof from about 10:1 to about 400:1, preferably from about 15:1 to about60:1.

Both the cocatalyst and the polymerization promoter may be introducedinto the reactor dissolved in an inert liquid solvent i.e.. a solventwhich is nonreactive with all the components of the catalyst system aswell as all the components of the reaction system. Hydrocarbons such asisopentane, hexane, heptane, toluene, xylene, naphtha and mineral oilare preferred for this purpose. Generally, such solutions contain from 1weight percent to 75 weight percent of the cocatalyst and/or thepolymerization promoter. If desired, less concentrated or moreconcentrated solutions can be employed, or, alternatively, thecocatalyst and polymerization promoter can be added in the absence ofsolvent, or, if desired, suspended in a stream of liquified monomer.When a solvent is employed and polymerization is conducted in a fluidbed, the amount of solvent introduced into the reactor should becarefully controlled so as to avoid the use of excessive quantities ofliquid which would interfere with the operation of the fluidized bed.

The solvents employed to dissolve the cocatalyst and the polymerizationpromoter may also be employed to introduce the solid catalyst precursorinto the reactor. Higher boiling solvents, such as mineral oil, arepreferred for this purpose. While the solid catalyst precursor may alsobe introduced into the reactor in the absence of solvent or suspended inliquified monomer, such solvents may be employed to disperse the solidcatalyst precursor and facilitate its flow into the reactor. Suchdispersions generally contain from 1 weight percent to 75 weight percentof the solid precursor.

The alpha olefins which may be polymerized with ethylene contain from 3to 8 carbon atoms per molecule. These alpha-olefins should not containany branching on any of their atoms closer than two carbon atoms removedfrom the double bond. Suitable alpha-olefins include propylene, butene1, pentene 1, hexene-1, 4-methyl-pentene-1, heptene-1 and octene-1.

The temperature employed can vary from about 10° C. to about 115° C.,preferably from about 80° C. to about 110° C., when polymerization iseffected in gas phase or in a slurry, and from about 150° C. to about250° C. when polymerization is effected in a solution. Whenpolymerization is conducted in a fluid bed, the temperature, of course,must be maintained below the sintering temperature of the polymersproduced in order to prevent polymer agglomeration.

The pressure employed can vary from subatmosphere to superatmosphere.Pressures of up to about 7000 kPa, preferably of from about 70 kPa toabout 3500 kPa, are suitable for gas phase, slurry and solutionpolymerizations.

If desired, polymerization may be conducted in the presence of an inertgas, i.e., a gas which is nonreactive under the conditions employedduring polymerization. The reactor should, however, be maintainedsubstantially free of undesirable catalyst poisons, such as moisture,oxygen, carbon monoxide, carbon dioxide, acetylene, and the like.

When polymerization is conducted in a fluid bed, the superficial gasvelocity of the gaseous reaction mixture through the bed must exceed theminimum flow required for fluidization in order to maintain a viablefluidized bed.

The following Examples are designed to illustrate the process of thepresent invention and are not intended as a limitation upon the scopethereof.

The properties of the polymers produced in the Examples were determinedby the following test methods:

Density

A plaque is made and conditioned for one hour at 120° C. to approachequilibrium crystallinity and is then quickly cooled to roomtemperature. Measurement for density is then made in a density gradientcolumn, and density values are reported as grams/cm³.

Melt Index (MI)

ASTM D 1238, Condition E. Measured at 190° C. and reported as grams per10 minutes.

Flow Index (FI)

ASTM D-1238, Condition F. Measured at 10 times the weight used in themelt index text above.

Melt Flow Ratio (MFR)

Ratio of Flow Index : Melt Index.

Activity

Activity values are normalized values based upon grams of polymerproduced per mmol of vanadium in the catalyst per hour per 100 psi ofethylene polymerization pressure.

EXAMPLE 1 Impregnation of Carrier with VCl₃ /THF Reaction Product

To a flask equipped with a mechanical stirrer were added 4 liters ofanhydrous tetrahydrofuran (THF), followed by 50 grams (0.318 mole) ofsolid VCl₃. The mixture was heated under nitrogen at a temperature of65° C. for 5 hours with continuous stirring in order to completelydissolve the VCl₃.

Eight hundred grams (800 g) of silica gel were dehydrated by heatingunder nitrogen at a temperature of 600° C. for 20 hours. The dehydratedgel was added to the solution prepared as above, and the mixture wasrefluxed for one hour under nitrogen. At the end of this time, themixture was heated at a temperature of 55° C. for about 6 hours under apurge of dry nitrogen to produce a dry, free-flowing powder containingabout 8 weight percent THF.

EXAMPLE 2 Treatment of Carrier with Diethylaluminum Chloride

Five hundred grams (500g) of the silica carrier impregnated with VCl₃/THF reaction product in accordance with Example 1 were slurried in 4liters of anhydrous hexane. The slurry was continuously stirred while a10 weight percent solution of diethylaluminum chloride in anhydroushexane was added over a period of 30 minutes. The impregnated carrierand the diethylaluminum chloride solution were employed in amounts thatprovided a desired atomic ratio of aluminum to vanadium. After additionof the diethylaluminum chloride solution was complete, the mixture washeated at a temperature of 45° C. for about 6 hours under a purge of drynitrogen to produce a dry, free-flowing powder.

EXAMPLE 3 Treatment of Carrier with MWD Regulator

Five grams (5.0 g) of the silica carrier treated with diethylaluminumchloride in accordance with Example 2 were slurried in 30 ml ofanhydrous hexane. The slurry was continuously stirred while a one molarsolution of a phosphorus-containing molecular weight distribution (MWD)regulator in anhydrous hexane was added over a period of 5 minutes.After addition of the solution was complete, the mixture was stirred foran additional 30-60 minutes. At the end of this time, the mixture washeated at a temperature of 50° C. either under vacuum or under a purgeof dry nitrogen to remove the hexane diluent and produce a free-flowingpowder.

The procedure was repeated a number of times with various amounts ofphosphorus-containing MWD regulators.

Table I below sets forth the particular phosphorus-containing MWDregulators employed in each of these experiments, as well as the molarratio of MWD regulator to vanadium present in the treated carrier.

                  TABLE I                                                         ______________________________________                                                                   Mol. Ratio MWD                                                                Regulator to V in                                  Example 3  MWD Regulator   Treated Carrier                                    ______________________________________                                        (a)        Tributylphosphine oxide                                                                       3.7                                                (b)        Triethyl phosphate                                                                            4.0                                                (c)        Tributylphosphine oxide                                                                       1.6                                                (d)        Tributylphosphine oxide                                                                       3.0                                                (e)        Tributylphosphine oxide                                                                       3.8                                                (f)        Triethyl phosphate                                                                            3.9                                                ______________________________________                                    

EXAMPLES 4-15

Slurry Polymerization

The solid catalyst components prepared as described in Example 3 wereemployed together with an alkylaluminum compound, as cocatalyst, and ahalohydrocarbon compound, as polymerization promoter, to co polymerizeethylene and hexene-1 in a one-liter autoclave reactor.

In each polymerization, the three catalyst components were pre mixed ina 6 ounce bottle containing 100 ml of hexane before being added to thereactor. Twenty milliliters (20.0 ml) of hexene-1 were added to thepre-mixed catalyst components before the resulting mixture wastransferred to the reactor. Anhydrous conditions were maintained at alltimes.

The polymerization reactor was dried by heating at 96° C. under a streamof dry nitrogen for 40 minutes. After cooling the reactor to 50° C., 500ml of hexane were added to the reactor, and the reactor contents werestirred under a gentle flow of nitrogen. The premixed catalystcomponents were then transferred to the reactor under a stream ofnitrogen and the reactor was sealed. The temperature of the reactor wasgradually raised to 60° C. and the reactor was pressurized with hydrogento a pressure of 10 kPa. The temperature was then raised to 75° C. andthe reactor was pressurized to 1050 kPa with ethylene. Heating wascontinued until the desired polymerization temperature of 85° C. wasattained. Polymerization was allowed to continue for 30 minutes, duringwhich time ethylene was continually added to the reactor to maintain thepressure constant. At the end of 30 minutes, the reactor was vented andopened.

Table II below sets forth the details involving the composition of thecatalysts employed in these polymerizations, as well as the reactionconditions employed during polymerization, the properties of thepolymers produced, and the productivity of each catalyst system.

Shorthand designations employed in Table II are defined as follows:

    ______________________________________                                        Designation     Definition                                                    ______________________________________                                        THF             Tetrahydrofuran                                               DEAC            Diethylaluminum chloride                                      TBPO            Tributylphosphine oxide                                       TEOPO           Triethyl phosphate                                            TEAL            Triethylaluminum                                              TIBA            Triisobutylaluminum                                           TNHAL           Tri-n-hexylaluminum                                           ______________________________________                                    

COMPARATIVE EXAMPLES A-C

For comparative purposes, ethylene was copolymerized with hexene 1 as inExamples 4-15 employing the solid catalyst component prepared inaccordance with Example 2, i.e., the catalyst component employed had notbeen treated with the MWD regulator as in Example 3. The details ofthese polymerizations are set forth in Table II below along with thedetails of Examples 4-15.

                                      TABLE II                                    __________________________________________________________________________                   Comp.             Comp.                                        EXAMPLE        Exp. A                                                                              4     5     Exp. B                                                                              6     7     8     9                    __________________________________________________________________________    Catalyst                                                                      Carrier        SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2                                                                           SiO.sub.2            Precursor      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                      VCl.sub.3 /THF       Modifier       DEAC  DEAC  DEAC  DEAC  DEAC  DEAC  DEAC  DEAC                 Modifier/V Ratio                                                                             1.1   1.1   1.1   2.6   2.6   2.6   2.6   2.6                  MWD Regulator  --    TBPO  TEOPO --    TBPO  TBPO  TBPO  TBPO                 MWD Regulator/V Ratio                                                                        --    3.7   4.0   --    1.6   1.6   1.6   3.0                  Cocatalyst     TEAL  TEAL  TEAL  TEAL  TEAL  TIBA  TNHAL TEAL                 Al/V Ratio     40    40    40    40    40    40    40    40                   Promoter       CFCl.sub.3                                                                          CFCl.sub.3                                                                          CFCl.sub.3                                                                          CHCl.sub.3                                                                          CHCl.sub.3                                                                          CHCl.sub.3                                                                          CHCl.sub.3                                                                          CHCl.sub.3           Promoter/Al Ratio                                                                            1.0   1.0   1.0   1.0   1.0   1.0   1.0   1.0                  Reaction Conditions                                                           Temperature, °C.                                                                      85    85    85    85    85    85    85    85                   Pressure, kPa  1050  1050  1050  1050  1050  1050  1050  1050                 Reaction Time, minutes                                                                       30    30    30    30    30    30    30    30                   Polymer Properties                                                            Density, g/cm.sup.3                                                                          0.952 0.942 0.945 0.944 0.943 --    0.944 0.945                Melt Index, g/10 min.                                                                        1.2   2.2   2.4   1.2   5.3   1.0   1.4   2.7                  Flow Index, g/10 min.                                                                        90    92    125   88    233   40    76    116                  Melt Flow Ratio                                                                              75    42    52    73    44    40    54    43                   Activity                                                                      g polymer/mmol 820   1671  1336  3705  5405  5118  7636  4687                 V-Hr-100 psi C.sub.2 H.sub.4                                                  __________________________________________________________________________                                   Comp.                                          EXAMPLE           10    11     Exp. C                                                                              12     13    14     15                   __________________________________________________________________________    Catalyst                                                                      Carrier           SiO.sub.2                                                                           SiO.sub.2                                                                            SiO.sub.2                                                                           SiO.sub.2                                                                            SiO.sub.2                                                                           SiO.sub.2                                                                            SiO.sub.2            Precursor         VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                       VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                       VCl.sub.3 /THF                                                                      VCl.sub.3 /THF                                                                       VCl.sub.3 /THF       Modifier          DEAC  DEAC   DEAC  DEAC   DEAC  DEAC   DEAC                 Modifier/V Ratio  2.6   2.6    4.5   4.5    4.5   4.5    4.5                  MWD Regulator     TBPO  TBPO   --    TBPO   TBPO  TEOPO  TEOPO                MWD Regulator/V Ratio                                                                           3.0   3.0    --    3.8    3.8   3.9    3.9                  Cocatalyst        TIBA  TNHAL  TEAL  TEAL   TIBA  TEAL   TIBA                 Al/V Ratio        40    40     40    40     40    40     40                   Promoter          CHCl.sub.3                                                                          CHCl.sub.3                                                                           CFCl.sub.3                                                                          CFCl.sub.3                                                                           CFCl.sub.3                                                                          CFCl.sub.3                                                                           CFCl.sub.3           Promoter/Al Ratio 1.0   1.0    1.0   1.0    1.0   1.0    1.0                  Reaction Conditions                                                           Temperature, °C.                                                                         85    85     85    85     85    85     85                   Pressure, kPa     1050  1050   1050  1050   1050  1050   1050                 Reaction Time, minutes                                                                          30    30     30    30     30    30     30                   Polymer Properties                                                            Density, g/cm.sup.3                                                                             --    0.944  0.944 0.944  0.944 0.945  0.941                Melt Index, g/10 min.                                                                           5.3   0.5    1.6   0.5    1.4   1.4    1.7                  Flow Index, g/10 min.                                                                           201   27     98    27     59    77     77                   Melt Flow Ratio   38    56     61    50     42    55     45                   Activity                                                                      g polymer/mmol V-Hr-100 psi C.sub.2 H.sub.4                                                     5716  7307   2839  3824   4348  3022   4559                 __________________________________________________________________________

We claim:
 1. In a process for homopolymerizing ethylene, orcopolymerizing ethylene with one or more alpha olefins containing from 3to 8 carbon atoms, with a catalyst system comprising(A) a solid catalystprecursor consisting essentially of(1) a solid, particulate, porous,inorganic carrier, as support for (2) the reaction product of (a) avanadium trihalide and (b) an electron donor, and (3) a boron halide oralkylaluminum modifier, (B) an alkylaluminum cocatalyst, and (C) ahalohydrocarbon polymerization promoter,the improvement which comprisestreating solid catalyst precursor (A) with a phosphorus-containingmolecular weight distribution regulator having the formula

    R.sub.3 P=O

wherein: R is a monovalent hydrocarbon radical free of aliphaticunsaturation containing from 1 to 14 carbon atoms, or ORl wherein R¹ isa monovalent hydrocarbon radical free of aliphatic unsaturationcontaining from 1 to 14 carbon atoms.
 2. A process as in claim 1 whereinR and R¹ are alkyl radicals containing from 1 to 6 carbon atoms or arylradicals containing 6 carbon atoms.
 3. A process as in claim 2 whereinthe phosphorus-containing molecular weight distribution regulator is aphosphine oxide.
 4. A process as in claim 3 wherein thephosphorus-containing molecular weight distribution regulator istributylphosphine oxide.
 5. A process catalyst precursor as in claim 2wherein the phosphorus-containing molecular weight distributionregulator is a phosphate.
 6. A process catalyst precursor as in claim 5wherein the phosphorus-containing molecular weight distributionregulator is triethyl phosphate.